The invention relates to linear bearings, such as used in heavy equipment, which provide linear load support and guidance particularly in applications where the area loads are too high to utilize the support and guidance through other kinds of rotational bearing elements, for example, due to the fact that the high area loads and resulting Hertzian stresses created in the contact zone would result in plastic deformation.
Linear bearing are used to support the lateral movement requested by the various processes and equipment such as bearing plates in mill windows of steel rolling mills. The bearing surfaces of those bearing plates are normally exposed to three major wear factors which include area loads, abrasion and corrosion. Wear, abrasion and corrosion typically lead to changes in the bearing plate geometry.
Abrasion and corrosion effectively increase the gap or play between two matching bearing surfaces and this increased play undesirably allows for relative movement of the equipment components. Due to the high dynamic energy of the moving components, the dynamic loads are proportional to the bearing play or gap. When dynamic loads reach a specific level, bearing plates transfer dynamic loads to bearing mounting and reference surfaces. The gap quickly grows and the output quality of the mill stand quickly degrades.
A direct relation between the hardness and stiffness of the material used for the bearing plates exists, because the hardness of any material is directly proportional to the stiffness and inflexibility of the material. A harder bearing plate material will deform a softer counterpart and as soon as the hardness of the bearing plate exceeds the hardness of the related mounting surface, the bearing plate will apply dynamic loads to its mounting counterpart with the potential to elastically and plastically deform the mounting surface. With this resulting deformation the connection between the bearing plate and the mounting surface will gradually yield gaps. These gaps permit, through a capillary effect, humidity and wetness to seep between the matching surfaces of the bearing.
Humidity and wetness between the matching surfaces, e.g., between the bearing plate and the mounting surface, will initiate another wearing factor called contact corrosion. Both mounting surfaces start transforming iron into iron oxide which then is washed out by more humidity pumped in by the relative movement under the constant dynamic loads created by the process. The result is a constantly increasing play or gap not only between the matching bearing surfaces of the equipment components involved but also between the bearing plates and their related mounting surfaces.
With sufficient moisture, a liquid layer is formed between the bearing plates and their related mounting surfaces. When high dynamic loads are applied to this liquid layer, cavitation occurs and leads to another wear mechanism. Cavitation increases the washout of the mounting surfaces which in turn gradually changes the geometry of those mounting surfaces. Due to the fact that mounting surfaces are at the same time the reference surfaces for the installation of the linear bearing plates, the equipment is gradually altered from its desired geometrical set-up.
Changes of the basic equipment geometry, for example a window of a rolling mill, will have a direct influence on the basic function of the equipment. In case of a rolling mill the changes of the mill window geometry change the geometrical relation of the rolls to each other which then in return has a direct influence on the rolling process as well as the geometry of the rolled products.
When any combination of the given process related limits are exceeded, the mill window geometry and reference base for the bearing plates has to be corrected. For such corrections there have been two basic processes. Prior to the present invention the play, gap or volume created be the erosion and wear and tear have been compensated by filling the gap with shims or injecting an appropriate resin material. Next, the surfaces are re-machined to new accuracy and the increased opening of the mill window compensated with the increasing of the bearing plate thickness. The selection of the correction method is driven by cost and time because the complete rolling mill has to be fully stopped to be able to apply the desired compensation technology. The quickest and cheapest approach has often been shimming or filling with resin and finally re-machining.
The prior art approach of applying the resin included steps of first mechanically adjusting the bearing plate geometry by using a combination of thrust and tension screws to provide a specific spacing between the bearing and mounting surface. Next, a seal was provided to surround the bearing plate and finally resin was injected between the bearing plate and the adjacent mounting surface. FIG. 10 illustrates such a process wherein a resin material 200 is injected between the housing liner 202 and the housing body 204. The resin material is injected under pressure and is maintained by a seal structure 206 surrounding the housing liner 202. The injected resin material 200 fills the interior volume defined between the housing liner 202 and the worn surface of the housing body 204. The success and durability of this methodology is strongly dependant on the preparation and cleanliness of the surfaces which are in direct contact with the resin. Due to the extremely hostile environment of the equipment to be repaired, the constant presence of oil and grease and also the dimensions and mostly vertical orientation of the mounting surfaces, it is very difficult to insure cleanliness of the resin-engaging surfaces necessary for rehabilitation of the bearing system. Due to the fact the resin has to be injected it has to be based on a 2-component epoxy which also needs a specific environmental temperature to be correctly applied. Also desirable temperature conditions for resin-setting are difficult, if not impossible, to maintain under the normal conditions of the facility.
There exist several negative effects of the application of plastic filling material or resin on the mounting surfaces of the mill housing body. Due to the difficulty of cleaning the mounting surface of the housing body, the contact between the resin and the worn out mounting surface is often not adequately maintained. Subsequent dynamic loads on the bearing plate further open a gap or create contact zones between the resin and the mounting surface allowing chemicals and liquid to seep in and cause corrosion. The plastic filling material or resin may also form bubbles which promote de-lamination and corrosion.
Thus, a need exists for a safe, economically efficient and robust approach so as remove the limitations of the prior art approaches to bearing maintenance and operation, particularly for linear bearings operating in hostile environments.